1. Field of the Invention
The present invention relates to a camera capable of switching an image record mode.
2. Description of the Related Art
As an example of related art of a camera having an image record mode switching function, a “black-and-white/color switching camera” is disclosed in JP-A-2001-45512. This camera employs a CCD as a solid-state image pick-up element. The sensitivity characteristics of the CCD have such characteristics as shown by a curve a shown in FIG. 6. When the camera is used as a color camera, since the wave length up to about 650 nm can be sensed by the eyes of a human being and a color reproducibility needs to be improved, an infrared radiation cut filter is arranged in the front surface of the CCD. The sensitivity characteristics of the CCD at this time are shown by a curve b shown in FIG. 6. On the other hand, when the camera is used as a black-and-white camera, since the improvement of sensitivity and the color reproducibility are hardly affected, the infrared radiation cut filter is removed.
Here, for instance, when a color mode shifts to a black-and-white mode (in the evening or it is assumed that the luminance of an interior lighting falls), after an image recording mode is decided on the basis of a luminance value, the infrared radiation cut filter is removed. At this time, as apparent from FIG. 6, an image pick-up signal in an infrared radiation area (720 nm or higher) is also added, so that the sensitivity is temporarily raised to increase the luminance value of the image pick-up signal, and, what is called a hunting phenomenon is generated in which a series of operations (a color mode to a black-and-white mode to a color mode to . . . ) that the image recording mode is apt to shift to an original color mode are repeated. This hunting phenomenon is likewise generated when the black-and-white mode shifts to the color mode (at dawn or it is assumed that the luminance of an interior lighting increases). In the black-and-white/color switching camera disclosed in the above publication, for preventing the hunting operation, one threshold value of a luminance level (it is abbreviated as Y1, hereinafter) when the black-and-white mode is switched to the color mode and two threshold values of a luminance level (they are abbreviated as Y2 and Y3, hereinafter) when the color mode is switched to the black-and-white mode are provided and the threshold values are respectively set to satisfy the relations that Y2 is larger than Y1, Y3 is larger than Y1 and Y2 is not equal to Y3 to prevent the hunting.
However, in the black-and-white/color switching camera of the related art, since the luminance levels upon recording an image under the black-and-white mode are greatly different depending on the presence or absence of illumination light and the kinds thereof, the respective threshold values, that is, Y1, Y2 and Y3 cannot be properly determined with ease and a hunting phenomenon cannot be inconveniently assuredly prevented.